1. Field of the Invention
The present invention relates to a shock absorbing underframe structure for railroad car use which relieves the shock of a collision.
2. Description of the Related Art
The conventional underframe of a railroad car is designed to relieve the stresses generated under various design loads such as vertical load, end-to-end compression load, torsional load, etc. within specification limits of strength so as to prevent plastic deformation. In addition, from rigidity considerations, the underframe is so designed that deformations under such loads will be within specified displacement values. This is a design concept with emphasis placed on strength and rigidity and constitutes a common practice in designing a railroad car frame structure inclusive of the underframe. It is a classical leading principle in the design of structures which is based on the password "acceptable if rugged".
However, in view of the comparatively high incidence of collisions, the recent railroad car specifications, particularly the specifications for light-weight streetcars represented by the low-floor articulated car call for "collision-destructibleness" in lieu of the time-honored "non-destructible" structure. This concept was proposed because, in the conventional "non-destructible" construction, the degree of damage to the front end of the frame structure on the occasion of a collision is low but, instead, the car undergoes a sudden stop or rebounds with the front end more or less intact and hence imposes a remarkably great acceleration-deceleration load on the passengers aboard to inflict serious and even fatal damages. Since, in such a mere "rugged" construction, the front end structure is hardly destroyed by a collision, the amount of shock energy that can be absorbed as the plastics train energy of the structure is considerably small so that the shock can not be effectively attenuated.
Designed to obviate the above disadvantages of the prior art structure in association with a collision , the present invention has for its object to provide a shock absorbing underframe structure for railroad car use which is characterized in that the shock of a collision is attenuated for protection of passengers through an "easily destructible" structure locally built into the underframe.
For the reasons mentioned below, the underframe of a railroad car must be a "non-destructible" structure withstanding predetermined magnitudes of vertical load, end-to-end compression load, torsional load, and car-end lifting load. It is also necessary that the underframe structure be readily adapted to a variety of cars varying in shock resistance load.